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  '64 1/2 to '73 -- The Classic Mustang
  Speedo gear

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Author Topic:   Speedo gear
JT
Gearhead

Posts: 200
From: Pearland, Texas, USA
Registered: Oct 2000

posted 05-04-2001 04:41 AM     Click Here to See the Profile for JT     Edit/Delete Message   Reply w/Quote
Okay, I have another question. Does anyone know how to determine what size speedometer cable gear I need to correct my speedometer? I switched from 2.79 gears in my 8" to 3.25. I have a C-4 and P205/70R14's all the way round. My Speedo is way off. When it shows 70, I'm actually doing about 55. I figure there must be some way to calculate which speedo cable gear I need, other than trial and error.

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JT
'68 Coupe w/351W

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richard bohm
Gearhead

Posts: 373
From: tucson,az-luray,va
Registered: May 2001

posted 05-04-2001 05:14 AM     Click Here to See the Profile for richard bohm   Click Here to Email richard bohm     Edit/Delete Message   Reply w/Quote
you need slow down the speedo. you likely have a 16 tooth speedo gear and you need and 18 tooth gear. i had the same problem with my grand marquis.

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Scott302
Journeyman

Posts: 30
From: Livonia, MI, USA
Registered: Mar 2001

posted 05-04-2001 07:19 AM     Click Here to See the Profile for Scott302     Edit/Delete Message   Reply w/Quote
In our catalog in the speedometer section there is a formula to calculate the number of driven gear teeth you need for you particular application.

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JT
Gearhead

Posts: 200
From: Pearland, Texas, USA
Registered: Oct 2000

posted 05-04-2001 12:44 PM     Click Here to See the Profile for JT     Edit/Delete Message   Reply w/Quote
Thanks Scott. I never noticed that in my NPD catalog. Now I just have to figure out how many teeth I have on the drive gear inside the tranny.

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richard bohm
Gearhead

Posts: 373
From: tucson,az-luray,va
Registered: May 2001

posted 05-05-2001 04:01 AM     Click Here to See the Profile for richard bohm   Click Here to Email richard bohm     Edit/Delete Message   Reply w/Quote
since you have a C4 i believe you have 7 teeth.

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mellowyellow
Gearhead

Posts: 6805
From: So. Fl.
Registered: Aug 2000

posted 05-05-2001 07:30 AM     Click Here to See the Profile for mellowyellow     Edit/Delete Message   Reply w/Quote
I think NPD has the best selection of speedo gears. I had that trouble with my 65 and I tried 3 gears. By a stroke of luck, I met a Fl Highway Patrol officer in a gas station. He clocked me at speeds up to 55 and I finally knew I had the right gear! And no ticket!!

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JT
Gearhead

Posts: 200
From: Pearland, Texas, USA
Registered: Oct 2000

posted 05-05-2001 08:15 PM     Click Here to See the Profile for JT     Edit/Delete Message   Reply w/Quote
From what I have seen NPD does have the best selection and prices. I think I'll get out my calculator and figure out which one to order. Thanks for all the advice.

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